Displaying specific records that match a specific criteria.

I have a number of records that I'm looping through, and i'm trying to flag out specific records that do not match the logic within my conditional. However whatever I've been trying, my results have been all of my records.

User.all.map do |u|
if [u.zip_code == true]
u.name
end
end

I feel elementary for asking this, but ultimately what i'm trying to do is flag any users that do not have a zip_code. With what I've done, is every record is displayed regardless of if I have my conditional equaling true or false.